1. Field of the Invention
This invention concerns precipitated calcium carbonate having a large surface area. More specifically, it concerns a novel process for preparing finely divided precipitated calcium carbonate having a large surface area and high purity. Additionally, this invention relates to large surface area, finely divided precipitated calcium carbonate coated with fatty acid derivatives. Further, this invention relates to filled polymeric compositions of matter wherein the filler comprises calcium carbonate of this invention alone or in addition to other fillers known in the art.
2. General Background
A process for precipitating calcium carbonate (calcite) by the carbonation of an aqueous lime slurry in the presence of certain organophosphorous compounds is disclosed in U.S. Pat. No. 4,367,207. The process disclosed in that patent concludes by the treatment of the carbonated slurry with sufficient polybasic acid to essentially neutralize any unreacted calcium hydroxide present. U.S. Pat. No. 4,367,207 teaches the production of calcium carbonate of an average particle size diameter of about 0.01 to 0.03 microns.
A process for producing uniform grain size calcium carbonate by reacting calcium carbonate having an average particle diameter of not more than 20 microns with acidic gas is disclosed in West German Patent No. 2,741,427. That process, however, requires that the acid gas be dehydrated before use as otherwise the calcium carbonate particles will join together and form lumps or aggregates.
Polyvinylchloride is a transparent polymer which becomes opaque when calcium carbonate having a small specific surface area is added as filler. In order for dispersion of calcium carbonate in polyvinylchloride polymers to occur, the calcium carbonate must be coated with a fatty acid derivative such as a salt of stearic acid. Even coated small specific surface area calcium carbonate imparts a large degree of opacity to polyvinylchloride polymers.